KR20070067968A - Method and apparatus for generating gamma voltage and liquid crystal display using the same and driving method thereof - Google Patents

Abstract

A method and an apparatus for generating a gamma voltage and an LCD device using the same and a driving method thereof are provided to simplify the circuit configuration by supplying high and low grayscale gamma voltages through one resistance string. An LCD(Liquid Crystal Display) device includes a liquid crystal panel, a power supplying unit, a gamma voltage generator, and a data driver. The liquid crystal panel displays images through plural sub-pixels, which include high and low grayscale regions. The power supplying unit generates a swing analog gamma voltage, which alternates between a first period for supplying a high analog gamma voltage and a second period for supplying a low analog gamma voltage. The gamma voltage generator generates and supplies plural high and low grayscale gamma voltages using the high and low analog gamma voltages, respectively. The data driver supplies a corresponding gamma voltage to the liquid crystal panel based on the first and second periods.

Description

METHOD AND APPARATUS FOR GENERATING GAMMA VOLTAGE AND LIQUID CRYSTAL DISPLAY USING THE SAME AND DRIVING METHOD THEREOF}

1 is a circuit block diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

FIG. 2 is a waveform diagram of a swing analog voltage output from the power supply unit shown in FIG. 1.

3 is a detailed circuit diagram illustrating a gamma voltage generator shown in FIG. 1.

FIG. 4 is a graph illustrating a gamma curve applied to the gamma voltage generator shown in FIG. 3.

FIG. 5 is a detailed circuit diagram of a part of generating a swing analog driving voltage in the power supply unit shown in FIG. 1. FIG.

<Description of Symbols for Main Parts of Drawings>

20: power supply unit 22: gamma voltage generator

24: Timing Controller 26: Data Driver

28: gate driver 30: liquid crystal panel

40: DC-DC converter

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display, and more particularly, to a method and apparatus for generating a gamma voltage for generating a two-tone gamma voltage for a gray-level combination of multi-domains, a liquid crystal display using the same, and a driving method thereof. It is about.

The liquid crystal display displays an image by driving liquid crystal molecules according to an electric field to adjust light transmittance. The liquid crystal display device includes a liquid crystal display panel (hereinafter referred to as a liquid crystal panel) for displaying an image through a liquid crystal cell matrix, and a driving circuit for driving the liquid crystal panel. The liquid crystal display is developing with a wide viewing angle technology in order to overcome a viewing angle limitation point in which an image is distorted depending on a position of a screen.

As a representative wide viewing angle technology of the liquid crystal display, a multi-domain VA (Multi-domain Vertical Alignment) mode is used. In VA mode, liquid crystal molecules having negative dielectric anisotropy are vertically oriented and driven perpendicular to the electric field direction to adjust light transmittance. In the VA mode, when the voltage is not applied, light transmission is blocked by a polarizer orthogonal to the alignment direction of the liquid crystal molecules, thereby becoming a normally black mode. In particular, the multi-domain VA mode divides each sub-pixel into multi-domains and symmetrically arranges the liquid crystal molecules so that a change in transmittance occurs symmetrically to obtain a wide viewing angle.

Recently, a method for improving visibility by dividing each sub-pixel having a multi-domain into a high gradation region according to a high gradation gamma curve and a low gradation region according to a low gradation gamma curve to improve visibility by gradation mixing between two gradation regions is proposed. In this case, the liquid crystal display divides R, G, and B data into high gray and low gray data using a high gray gamma voltage set and a low gray gamma voltage set, and then divides the high gray region and the low gray level in each sub-pixel. An analog gradation conversion method respectively supplied to the gradation region is used. To this end, the conventional gamma voltage generator generates a high gray gamma voltage set including a plurality of gamma voltages using a high gray gamma string, and a low gray level including a plurality of low gray gamma voltages using a low gray gamma string. A gamma voltage set must be generated and output. In addition, the conventional gamma voltage generator must include an expensive switch for each gray level to select and output a high gray gamma voltage and a low gray gamma voltage. For this reason, the conventional gamma voltage generator has a complicated circuit configuration, which causes a rise in manufacturing cost.

Accordingly, an object of the present invention is to provide a gamma voltage generation method and apparatus capable of simplifying a circuit configuration of a gamma voltage generator, a liquid crystal display using the same, and a driving method thereof.

In order to achieve the above object, the gamma voltage generation method according to the present invention comprises the steps of generating and supplying a swing analog gamma voltage alternating a first period for supplying a high analog gamma voltage and a second period for supplying a low analog gamma voltage Wow; Generating a plurality of high gradation gamma voltages using the high analog gamma voltage supplied in the first period; Generating a plurality of low gray level gamma voltages using the low analog gamma voltages supplied in the second period. Here, the plurality of high gray gamma voltages and the plurality of low gray gamma voltages are generated through the same resistance string.

In addition, the gamma voltage generation device according to the present invention includes a power supply unit for generating a swing analog gamma voltage alternately between a first period for supplying a high analog gamma voltage and a second period for supplying a low analog gamma voltage; Generate and supply a plurality of high gray level gamma voltages using the high analog gamma voltage supplied in the first period, and generate a plurality of low gray level gamma voltages using the low analog gamma voltage supplied in the second period. And a gamma voltage generator for supplying the same.

The gamma voltage generator alternately generates the plurality of high gray gamma voltages and the plurality of low gray gamma voltages through a resistor string connected in series between the swing analog gamma voltage and the ground.

The power supply unit includes a reactance connected between an input terminal supplied with an input voltage and a first node supplied with an output voltage, and adjusts an amount of current passing through the reactance through an output switch controlled by a pulse width modulation signal. A DC-DC converter for supplying an output signal to one node; A rectifier for rectifying the output signal supplied to the first node of the DC-DC converter to supply the swing analog driving voltage to a second node; A feedback circuit for feeding back the voltage output to the second node to the DC-DC converter; The feedback circuit adjusts the duty ratio of the pulse width modulated signal by varying the voltage fed back to the DC-DC converter in the first and second periods so that the swing analog drive voltage is supplied to the second node.

A liquid crystal display according to the present invention comprises: a liquid crystal panel for displaying an image through a plurality of sub pixels divided into a high gradation region and a low gradation region; A power supply unit for generating a swing analog gamma voltage that alternates a first period of supplying a high analog gamma voltage and a second period of supplying a low analog gamma voltage; Generate and supply a plurality of high gray level gamma voltages using the high analog gamma voltage supplied in the first period, and generate a plurality of low gray level gamma voltages using the low analog gamma voltage supplied in the second period. A gamma voltage generator configured to supply the gamma voltage generator and a gamma voltage corresponding to data among the plurality of high gray gamma voltages in the first period, and a gamma voltage corresponding to data among the plurality of low gray gamma voltages in the second period. And a data driver for supplying the liquid crystal panel.

The liquid crystal panel causes a high gradation region of each of the sub-pixels to be driven in the first period, and a low gradation region of the sub-pixels to be driven in the second period, and the first and second periods alternately. Let it be repeated

The method of driving the liquid crystal display according to the present invention includes the steps of: generating a swing analog gamma voltage alternated between a first period of supplying a high analog gamma voltage and a second period of supplying a low analog gamma voltage; Generating and supplying a plurality of high gray level gamma voltages using the high analog gamma voltages supplied in the first period; Selecting a gamma voltage corresponding to data among the plurality of high gray gamma voltages in the first period and supplying the gamma voltages to a liquid crystal panel; Generating and supplying a plurality of low gray level gamma voltages using the low analog gamma voltages supplied in the second period; Selecting a gamma voltage corresponding to data among the plurality of low gray level gamma voltages in the second period and supplying the gamma voltage to the liquid crystal panel.

In addition, the driving method of the liquid crystal display according to the present invention comprises the steps of driving a high gradation region of each sub-pixel constituting the liquid crystal panel in the first period; Driving a low gradation region of each of the sub-pixels in the second period; And the first and second periods are alternately repeated.

Other objects and advantages of the present invention in addition to the above object will become apparent from the description of the preferred embodiment of the present invention with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to FIGS. 1 to 5.

1 is a circuit block diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

The liquid crystal display shown in FIG. 1 generates a gate driver 28 for driving the gate line GL of the liquid crystal panel 30, a data driver 26 for driving the data line DL, and a gamma voltage. Generates a gamma voltage generator 22 for supplying the data driver 26, a timing controller 24 for controlling the data driver 26 and the gate driver 28, and a plurality of driving voltages required for the circuit blocks. It is provided with a power supply unit 20 to supply.

The power supply unit 20 is supplied with a driving voltage VDD from the outside, and the driving voltage VDD is supplied to the timing controller 24 including the digital circuit, the data driver 26 and the gate driver 28 as a digital driving voltage. Supplied. The power supply unit 20 generates the gate-on voltage VON and the gate-off voltage VOFF by using the driving voltage VDD from the outside, supplies them to the gate driver 28, and generates a common voltage VCOM. Supply to the liquid crystal panel 30. In addition, the power supply unit 20 uses the input driving voltage VDD to convert the high analog driving voltage HAVDD and the low analog driving voltage LAVDD into a predetermined period, that is, a horizontal period H, as shown in FIG. 2. The alternating swing analog driving voltage VDD_SW is generated and supplied to the gamma voltage generator 22 and the data driver 26. A detailed description of a portion of generating the swing analog driving voltage VDD_SW in the power supply unit 20 will be described later.

The timing controller 24 controls a plurality of control signals for controlling the driving timing of the gate driver 28 and the data driver 26 by using externally inputted vertical synchronization signals, horizontal synchronization signals, dot clocks, data enable signals, and the like. Occurs. In addition, the timing controller 24 aligns the input data signal according to the dot clock signal and supplies it to the data driver 26.

The gamma voltage generator 22 generates a plurality of gamma voltages V0 to V63 by dividing the swing analog driving voltage AVDD_SW from the power supply unit 20 using the resistor string shown in FIG. 3 to generate the data driver 26. ). In detail, the gamma voltage generator 22 performs the high analog driving voltage through the resistance string shown in FIG. 3 in a horizontal period in which the high analog driving voltage HAVDD is input among the swing analog driving voltages AVDD_SW shown in FIG. 2. By dividing (HAVDD), a plurality of high gradation gamma voltages VH0 to VH63 are generated and supplied to the data driver 26. In this case, the high gray gamma voltage set including the plurality of high gray gamma voltages VH0 to VH63 output from the gamma voltage generator 22 follows the high gray gamma curve G_VH among the gamma curves shown in FIG. 4. . In the horizontal period in which the low analog driving voltage LAVDD is input, the gamma voltage generator 22 divides the low analog driving voltage LAVDD through the resistor string shown in FIG. VL63) is generated and supplied to the data driver 26. At this time, the low gray gamma voltage set including the plurality of low gray gamma voltages VL0 to VL63 output from the gamma voltage generator 22 follows the low gray level gamma curve G_VL among the gamma curves shown in FIG. 4. . As a result, the gamma voltage generator 22 alternates between the high gray gamma voltage (VH) and the low gray gamma voltage (VL) in units of horizontal periods while having only one resistance string by the swing analog driving voltage AVDD_SW. It becomes possible to supply to (26).

The data driver 26 selects a gamma voltage supplied through the gamma voltage generator 22 according to the digital data signal from the timing controller 24 and supplies the gamma voltage to the data line DL of the liquid crystal panel 30. At this time, the data driver 26 converts the R, G, and B data signals from the timing controller 40 into a high gradation data signal using a high gradation gamma voltage set in one horizontal period and supplies them to the liquid crystal panel 30. In the next horizontal period, the low gray level gamma voltage set is used to convert the low gray level data signal to be supplied to the liquid crystal panel 30.

The gate driver 28 generates a scan signal according to a control signal from the timing controller 24 and supplies the scan signal to the gate line GL. At this time, the gate driver 28 selects the gate-on voltage VON of the power supply unit 20 as a gate line GL scan signal according to the control signal from the timing controller 24, and supplies the gate-off voltage in the remaining period. Select (VOFF) to supply to the gate line GL.

The liquid crystal panel 30 includes R, G, and B sub-pixels each having a 1: 2 area ratio and having a vertically divided high and low gradation region VH and a low gradation region VL. The high gradation region VH and the low gradation region VL of each sub-pixel are driven by the respective thin film transistors TFT, and the upper and lower sides of the high gradation region VH and the low gradation region VL of the adjacent sub-pixels. Are staggered into. Accordingly, the high gradation region VH and the low gradation region VL of the R, G, and B subpixels are driven by being divided into a horizontal period in which the high gradation data signal is supplied and a horizontal period in which the low gradation data signal is supplied.

For example, the thin film transistor TFT connected to the first gate line GL1 is connected to the high gradation region VH of the R, G, and B sub pixels, and is connected to the second gate line GL2. The TFT is connected to the low gradation region VL of the R, G, and B sub pixels. Specifically, each of the TFTs connected to the first gate line GL1 and positioned in the R and B low gradation regions VL at the top thereof has R and B at the bottom thereof with the drain electrode thereof extended downward. It is connected to each of the high gradation regions VH. In addition, each of the thin film transistors TFT connected to the second gate line GL2 and positioned in the R and G high gradation regions VH at the bottom thereof, has a drain electrode thereof extended upward to have an R and B low gradation region at the top. (VL) is connected to each. The thin film transistor TFT connected to the first gate line GL1 and positioned in the G high gradation region VH at the upper end thereof is connected to the G high gradation region VH, and is connected to the second gate line GL2. The thin film transistor TFT connected to and positioned in the lower G low gradation region VL is connected to the G low gradation region VL.

Accordingly, in the 1H period during which the first gate line GL1 is driven, the high grayscale RH, GH, and BH data signals supplied from the data driver 26 to the first to third data lines DL1, DL2, and DL3 are generated. R, G, and B high gradation regions VH are respectively filled. Subsequently, the low grayscale RL, GL, and BL data signals supplied from the data driver 26 to the first to third data lines DL1, DL2, and DL3 in the 2H period during which the second gate line GL2 is driven are R. , G, and B low gradation regions VH are respectively filled. Accordingly, each of the R, G, and B sub-pixels has a gamma curve as shown in FIG. 3 in a combination of high gray and low gray according to the data signal charged in each of the high gray region VH and the low gray region VL. It will express gradation following G).

As described above, the gamma voltage generator 22 of the liquid crystal display according to the present invention uses the swing analog driving voltage AVDD_SW to horizontally set the high gray gamma voltage set and the low gray gamma voltage set through one resistance string. It can be generated alternately every time and supplied. Therefore, the circuit configuration of the gamma voltage generator 22 can be simplified.

FIG. 5 is a detailed circuit diagram of a part of generating the swing analog driving voltage AVDD_SW in the power supply unit 20 shown in FIG. 1.

The power supply unit 20 illustrated in FIG. 5 rectifies an output signal supplied to the first node N1 by the DC-DC IC 40, the DC-DC IC 40, and the reactance L, thereby reconstructing the second node. The diode D and the capacitor C supplied to the swing analog driving voltage AVDD_SW at N2 and the swing analog driving voltage AVDD_SW supplied to the second node N2 are divided into DC-DC ICs 40. The first and second resistors (R1, R2) to be fed back to), and the switch (SW) is selectively connected in parallel with the second resistor (R2) to vary the voltage fed back to the DC-DC IC (40) Three resistors R3 are provided.

The DC-DC IC 40 is driven by the driving voltage VDD supplied to the input terminal VIN to pulse width modulate the pulse signal oscillated therein to generate a modulated pulse signal. The DC-DC IC 40 switches the output switch connected to the output terminal SW by the modulated pulse signal so that the reactance L charges and discharges the current, thereby providing the input voltage VDD to the first node N1. Level is raised and the ripple component causes the output signal to be generated. The ripple component of the output signal generated at the first node N1 is rectified by a rectifier composed of a diode D and a capacitor C and output through the second node N2.

The first and second resistors R1 and R2 connected between the second node N2 and the ground GND divide the voltage AVDD_SW output to the second node N2 to divide the DC-DC IC 40. To the feedback terminal FB. The switch SW selectively connects the third resistor R3 with the second resistor R2 to vary the feedback voltage supplied to the feedback terminal FB of the DC-DC IC 40 so as to change the first node N1. The output voltage is variable. This is because the level of the signal output from the DC-DC IC 40 to the first node N1 depends on the feedback voltage input to the feedback terminal FB of the DC-DC IC 40. Specifically, an error amplifier built in the DC-DC IC 40 compares the feedback voltage input through the feedback terminal FB with a reference voltage and outputs the difference voltage, and the PWM modulator outputs the difference voltage according to the difference voltage of the error amplifier. This is because the voltage level output to the first node N1 is determined by modulating the pulse width from the control signal. The duty ratio of the pulse width modulated signal is varied according to the feedback voltage input to the feedback terminal FB of the DC-DC IC 40, and the switching speed of the output switch is varied according to the duty ratio of the pulse width modulated signal, thereby providing DC-DC. The output signal level of the IC 40 can be varied. At this time, the output signal level of the DC-DC IC 40 has a relationship inversely proportional to the duty ratio of the pulse width modulated signal (Vout = Vin / (1-Duty)).

For example, the switch SW is turned off and the voltage output to the second node N2 is divided by the first and second resistors R1 and R2 and input to the feedback terminal to the DC-DC IC 40. The feedback voltage then increases relatively. When the feedback voltage increases, the difference voltage with the reference voltage set in the DC-DC IC 40 decreases, and the duty ratio of the pulse width modulation signal increases so that the current output to the first node N1 decreases so that the output level decreases. do. Accordingly, the low analog driving voltage LAVDD is output to the second node N2. Then, the switch SW is turned on and the voltage output to the second node N2 is divided by the resistance ratio between the first resistor and the second and third resistors R2 // R3 connected in parallel. The feedback voltage fed back to the DC-DC IC 40 is relatively reduced. When the feedback voltage decreases, the difference voltage with the reference voltage set in the DC-DC IC 40 increases, and the duty ratio of the pulse width modulated signal decreases so that the current output to the first node N1 increases to increase the output level. do. Accordingly, the high analog driving voltage LAVDD is output to the second node N2. Accordingly, the switch SW connected to the feedback terminal of the DC-DC IC 40 is turned on / off in units of horizontal periods so that the second node N2 has a horizontal period H as shown in FIG. 2. It is possible to supply the swing analog driving voltage AVDD_SW that alternates the high analog driving voltage HAVDD and the low analog driving voltage LAVDD in units of).

As described above, the method and apparatus for generating gamma voltage according to the present invention, the liquid crystal display using the same, and the method for driving the same according to the present invention utilize a swing analog driving voltage to set a high gray scale gamma voltage and a low gray scale gamma voltage through one resistance string. Sets can be alternately generated and supplied every horizontal period. Therefore, it is possible to simplify the circuit configuration of the gamma voltage generator that outputs the high gray gamma voltage set and the low gray gamma voltage set.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (10)

Generating and supplying a swing analog gamma voltage that alternates a first period of supplying a high analog gamma voltage and a second period of supplying a low analog gamma voltage; Generating a plurality of high gradation gamma voltages using the high analog gamma voltage supplied in the first period; Generating a plurality of low gray level gamma voltages using the low analog gamma voltages supplied in the second period. The method of claim 1, And the plurality of high gray gamma voltages and the plurality of low gray gamma voltages are generated through the same resistance string. A power supply unit for generating a swing analog gamma voltage that alternates a first period of supplying a high analog gamma voltage and a second period of supplying a low analog gamma voltage; Generate and supply a plurality of high gray level gamma voltages using the high analog gamma voltage supplied in the first period, and generate a plurality of low gray level gamma voltages using the low analog gamma voltage supplied in the second period. And a gamma voltage generator for supplying the gamma voltage generator. The method of claim 3, wherein The gamma voltage generator And generating a plurality of high gray gamma voltages and a plurality of low gray gamma voltages alternately through resistance strings connected in series between the swing analog gamma voltage and ground. The method of claim 3, wherein The power supply unit A reactance connected between an input terminal to which an input voltage is supplied and a first node to which an output voltage is supplied, and controlling an amount of current passing through the reactance through an output switch controlled by a pulse width modulation signal to adjust the amount of current passing through the reactance to the first node. A DC-DC converter for supplying an output signal; A rectifier for rectifying the output signal supplied to the first node of the DC-DC converter to supply the swing analog driving voltage to a second node; A feedback circuit for feeding back the voltage output to the second node to the DC-DC converter; The feedback circuit may vary the voltage fed back to the DC-DC converter in the first and second periods to adjust the duty ratio of a pulse width modulated signal so that the swing analog drive voltage is supplied to the second node. Gamma voltage generator. A liquid crystal panel for displaying an image through a plurality of sub pixels divided into a high gradation region and a low gradation region; A power supply unit for generating a swing analog gamma voltage that alternates a first period of supplying a high analog gamma voltage and a second period of supplying a low analog gamma voltage; Generate and supply a plurality of high gray level gamma voltages using the high analog gamma voltage supplied in the first period, and generate a plurality of low gray level gamma voltages using the low analog gamma voltage supplied in the second period. A gamma voltage generator for supplying A data driver which selects a gamma voltage corresponding to data among the plurality of high gray gamma voltages in the first period and selects a gamma voltage corresponding to data among the plurality of low gray gamma voltages and supplies the same to the liquid crystal panel The liquid crystal display device characterized by the above-mentioned. The method of claim 6, The liquid crystal panel Driving a high gradation region of each sub-pixel in the first period, driving a low gradation region of the sub-pixels in the second period, and causing the first and second periods to be alternately repeated. A liquid crystal display device characterized by the above-mentioned. The method of claim 6, The power supply unit A reactance connected between an input terminal to which an input voltage is supplied and a first node to which an output voltage is supplied, and controlling an amount of current passing through the reactance through an output switch controlled by a pulse width modulation signal to adjust the amount of current passing through the reactance to the first node. A DC-DC converter for supplying an output signal; A rectifier for rectifying the output signal supplied to the first node of the DC-DC converter to supply the swing analog driving voltage to a second node; A feedback circuit for feeding back the voltage output to the second node to the DC-DC converter; The feedback circuit may vary the voltage fed back to the DC-DC converter in the first and second periods to adjust the duty ratio of a pulse width modulated signal so that the swing analog drive voltage is supplied to the second node. Liquid crystal display device. Generating a swing analog gamma voltage alternated between a first period of supplying a high analog gamma voltage and a second period of supplying a low analog gamma voltage; Generating and supplying a plurality of high gray level gamma voltages using the high analog gamma voltages supplied in the first period; Selecting a gamma voltage corresponding to data among the plurality of high gray gamma voltages in the first period and supplying the gamma voltages to a liquid crystal panel; Generating and supplying a plurality of low gray level gamma voltages using the low analog gamma voltages supplied in the second period; And selecting a gamma voltage corresponding to data among the plurality of low gray level gamma voltages in the second period to supply the gamma voltage to the liquid crystal panel. The method of claim 9, Driving a high gradation region of each sub pixel constituting the liquid crystal panel in the first period; Driving a low gradation region of each of the sub-pixels in the second period; And alternately repeating the first and second periods.

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